CacheManager - all or nothing?

From Intelligent Cache Management with WebCenter Sites - 11g Release 1 (11.1.1.8.0):

Utilizing CacheManager to flush the cache requires ceding full control over the lifecycle of rendering engine cache objects to CacheManager by specifying that the objects never expire from the cache. When CacheManager determines that they are obsolete because of changes in the underlying content (i.e., in one of the compositional dependencies recorded against each object), it removes those objects from the cache.


Note:
The reason for specifying an infinite expiration time is to ensure that CacheManager keeps a record of all objects that are cached, as well as what dependencies are tracked against them. This record is stored on WebCenter Sites, and it is linked to the existence of the cached object on the first tier. This record enables CacheManager to infer the existence of objects in the second tier cache and therefore flush the objects from the second tier cache.
If, however, an object were to expire from the cache, its record would be removed, leaving CacheManager without the information it requires to